The present invention relates to an apparatus for mixing fluids held in containers. Normally, this type of apparatus is used in a laboratory, and the fluids are held in test tubes. It is frequently desired to stir the fluids, for example, to mix two fluids together or to evenly disperse particulate matter in a liquid medium.
One device for mixing liquids known to the prior art is disclosed in the Kraft, et al U.S. Pat. No. 3,061,280 entitled "Apparatus for Mixing Fluent Material", issued Oct. 30, 1962. In this device, a test tube is held at its upper portion by means of a spring-type clamp which permits rotation of the lower end of the tube. The lower end of the tube is received in a deep resilient cup which is driven eccentrically by means of an electric motor. Although the apparatus disclosed in the patent cited above does not allow for variation in the intensity of stirring since the deep resilient cup is driven at constant angular velocity, nevertheless, the commercial version did provide a rheostat in the motor circuit which permitted speed control. In this commercial version, marketed under the trade name "Vortex Genie Mixer" by the owner of this application, the resilient clamp mounting for the upper neck of the test tube was also eliminated; and the holder for the tube was modified from a deep plastic foam holder to a shallow rubber cup. In operating this commercial device, a person held the test tube with one hand and placed the bottom of the tube into the shallow cup. He then pressed a switch which energized the motor, and, if desired, operated the rheostat to achieve the desired stirring speed.
It will be appreciated that more energy is normally required to start a true vortex of the fluid than is required to continue the stirring once it is started. That is, once the inertia of the fluid is overcome, unless the stirring energy is decreased, the fluid vortex may climb the side of the test tube and even spill over.
One of the disadvantages of this last-named system is that it requires two hands to operate--one to control the speed of rotation (by varying a rheostat), and the other to hold the tube in place. Speed control of a shaded pole induction motor by means of a rheostat is not positive, and the speed varies with the load on the motor for any given setting. Further, since the fluid vortex has a tendency to climb the walls of the test tube suddenly, once started, spillage has occurred. The possibility of spillage is further increased because the machine is normally turned on without adjusting the speed, and the speed at which it had been set may be too high for the viscosity and quantity of fluid desired to be stirred. In addition, pressing on the test tube causes a loading of the drive motor with resultant lowering of the mixing speed.
In one embodiment, the present invention provides an elongated cylinder mounted in a generally upright position by means of a gimbal mount located toward the top of the cylinder. The gimbal mount permits unrestricted rotation of the bottom of the cylinder which is driven by an eccentric drive. A receptacle is slidably mounted within the cylinder, and biased to an upward position by means of a coil spring. A switch is located in a position adjacent the gimbal mount, and it is actuated when a test tube containing fluids desired to be mixed is inserted into the cylinder and pressed downwardly to lower the receptacle against the action of the coil spring. When the switch is actuated, it starts a motor which then drives the base of the cylinder in circular motion at a constant angular velocity.
The axis of the cylinder can therefore be thought of as forming a conical surface as it rotates; and as the test tube is further lowered into the cylinder, held by the receptacle or cup, the intensity of the stirring motion increases because the circumference through which the base of the test tube is rotated enlarges, according to the shape of the cone formed by the axis of the cylinder, as just described. Hence, the intensity of the stirring action can be controlled simply by moving the test tube axially of the cylinder.
The present invention eliminates the need for a speed control mechanism in the drive motor while providing a smooth, controllable and predictable variation in stirring intensity. Constant stirring speed is quickly achieved, and the stirring intensity may be reduced by withdrawing the test tube slightly with the motion of a single hand. The possibility of spillage is thus greatly reduced and overall control is smoother and achieved with only one hand.
Another feature of the present invention is that the cup for holding the test tube is provided with a generally conical surface on which the test tube is seated; and the lower portion of this conical surface is provided with an aperture. The interior of the cylinder may be cleaned by introducing a cleaning solution through the hole and pumping the solution through the cylinder and a flexible conduit which couples any fluid in the cylinder outside the device.
Another feature of the present invention is that pressing down firmly on the test tube does not load the motor significantly--it merely lowers the receptacle for the test tube down into the driven cylinder and increases the intensity of the stirring action. That is to say, it does not load the motor to slow it down, as with the device mentioned.
With the present invention, then, stirring action is initiated by placing a test tube into the cup at the top of the cylinder and lowering it. Downward displacement of the cup actuates a switch which drives the base of the cylinder in rotary motion at constant angular velocity. The top of the cylinder is constrained by the gimbal mount. As the test tube is inserted more deeply into the cylinder, a vortex will be formed by the fluid in the tube. The intensity of the stirring action may be increased if the test tube is lowered further; and conversely, as it is withdrawn, the intensity of the stirring action abates until the cup reaches its original position and turns off the drive motor. All control is thus achieved with a single hand motion.
An appliance is also disclosed which may be attached to the apparatus and easily removed for providing a vibrating platform, if desired.